Last year, Nigeria reported only 250 cases (likely a substantial under count) and 8 deaths. By contrast - in 2012 - 117 deaths were recorded.

Lassa isa Viral Hemorrhagic Fever
(VHF), although it is nowhere near as virulent as Ebola or Marburg. The Lassa virus is commonly carried by multimammate rats, a local rodent that often likes to enter
human dwellings.

Exposure is typically through the urine or dried feces of infected rodents, and roughly 80% who are infected only experience mild symptoms. The overall mortality rate is believed to be in the 1%-2% range, although it runs much higher (15%-20%) among those sick enough to be hospitalized.

Like many other hemorrhagic fevers, person-to-person transmission may
occur with exposure to the blood, tissue, secretions, or excretions of
an individual, although the CDC reassures:

Casual contact (including skin-to-skin contact without exchange of
body fluids) does not spread Lassa virus. Person-to-person transmission
is common in health care settings (called nosocomial transmission) where
proper personal protective equipment (PPE) is not available or not
used. Lassa virus may be spread in contaminated medical equipment, such
as reused needles.

Over the past couple of days alarm bells have started ringing in Nigeria as it was revealed that 86 Lassa cases have been reported from 10 states over the past 6 weeks, and of those, 40 have died.

While this high mortality rate is getting a lot of press, this is a relatively small sample, there is often a bias towards identifying the most critically ill subset of patients early in any outbreak, and that there may be unreported co-factors at work here.

All of which could help to skew the mortality figures higher.

Forty deaths in such a short time period, however, is a substantial jump over recent years. Last night (Friday), the Health Minister Isaac Adewole, speaking at a news conference, announced the latest case counts and called the number of deaths `unusual'.

The twitter hashtag #Lassafever is seeing a lot of traffic overnight, with @EbolaAlert posting public health infographics and links.

While Lassa is unlikely to spark a major epidemic, the same could have been said for Ebola a couple of years ago. Of late - when it comes to infectious diseases - conventional wisdom has suffered some setbacks.

So we'll keep an eye on this outbreak, and I'll report back any significant information.